Comparative genomics of Pseudomonas spp. Isolated from Antarctica: Insights into High Levels of Extracellular Maltodextrin Production

Maltodextrins, currently produced from cornstarch and partially by synthetic methods, are widely used in medicine and foods as excipients and additives, respectively. We recently isolated a Pseudomonas spp. from the Chilean Antarctic Territory (isolate P198; from soil; King George’s Island), which constitutes the first example of a microorganism producing and secreting maltodextrin. P198 can use glycerol as the only carbon source at temperatures ranging from 4 to 28 ºC, which makes it suitable for future biotechnology applications. In this study, we present genomic analyses that were conducted in order to identify and characterize P198. We isolated P198 on solid media (LB and King’s b). On King’s b, P198 produced and secreted a poly saccharide that was later confirmed by HPLC to be maltodextrin. Based on morphology, culture growth, and biochemical battery (not shown), we identify P198 as a member of Pseudomonas genus, possibly related to the fluorescens group. Additionally, we sought to identify P198 based on genomic features for which we sequenced and de novo assembled its genome yielding 126 contigs (N50 = 213954). Sequence comparisons against four kingdom-wide markers (16S rRNA, RecA, RpoB, and groEL) confirmed that P198 belonged to the Pseudomonas genus. We categorized P198’s genes by COG function and noted that ~500 out of 6413 predicted genes were of unknown function. We compared P198 against a representative set of 87 Pseudomonas genomes representing the breath of the genus’ phylogenetic diversity. Among all 87 isolates, average nucleotide identity ranged between 82 and 94.5%. The most similar isolates were Pseudomonas sp. PAMC 26793 (94.5%) and Pseudomonas fluorescens BBc6R8 (93.7%). The former was reportedly isolated from grasslands in northern Alaska, and the latter from soil (associated with fungus sporocarp). However, phenotypically P198 was more similar to the wrinkle spreader phenotype of Pseudomonas fluorescens SBW25 (87.5% similar to P198; isolated from soil). Using SBW25 as reference, we observed extensive genomic rearrangements (mosaicism) on PAMC, BBc6R8, and P198 as well as extensive regions of indels (up to 50 kb) on P198. Pangenome analysis revealed extensive gene diversity among the 88 Pseudomonas isolates reinforcing the notion that the group is highly variable. The ‘cloud genome’ was > 44000 genes, while the ‘shell’ and ‘core’ genes were 5367 and 505 genes, respectively. In agreement with the phenotypic resemblance between P198 and SBW25, the number of unique genes in P198 against SBW25 were only 33, in contrast to 347 and 213 genes when comparing against PAMC and BBc6R8, respectively. This preliminary study, enables us to inquire P198’s genome to unravel the underlying genetic determinants of maltodextrin production and secretion.